1. Field of the Invention
The invention in general relates to the field of medical pneumatic tourniquets, and more particularly to a tourniquet which is automatically controlled to maintain the desired tourniquet pressure.
2. Description of the Prior Art
Tourniquets are used in medicine to stop the flow of blood into a patient's limb. A typical use is to provide a "bloodless field" in which surgical procedures may be performed on a limb, without the field being obscured by blood, and without loss of blood to the patient. Tourniquets are also used in emergency procedures to prevent loss of blood when a limb is damaged or in any other instance where it is desired to prevent blood flow to a limb.
Tourniquets conventionally consist of an inflatable cuff which is wrapped around the patient's limb, and a source of compressed gas for inflating the cuff. In order to successfully stop the flow of blood the pressure in the cuff must be above the highest level of the patient's blood pressure. However, it should not be so high that it damages the tissue of the limb. Thus in conventional tourniquets a pressure gauge for measuring the cuff pressure, and a pressure regulating mechanism is provided.
Up until very recently, conventional pneumatic tourniquets have been manually controlled mechanical devices. That it, a mechanical pressure regulating mechanism indicated the pressure and the pressure was adjusted by an attendant using a mechanical valve.
Recently, an automatic tourniquet for medical use has been created by Dr. James A. McEwen. This tourniquet is described in U.S. patent application Ser. No. 193,145 filed Oct. 2, 1980. An improved automatic tourniquet is described in U.S. patent application Ser. No. 337,152 filed Jan. 5, 1982, also by Dr. James McEwen. In these automatic tourniquets, the pressure in the cuff is continuously sensed and adjusted by a microprocessor. In addition, the microprocessor activates alarms if a dangerous pressure condition is sensed. It has been found that such automatic tourniquets systems not only are much more convenient in the operating room setting, but also significantly reduce the incidence of limb paralysis, nerve damage and other injuries attributable to tourniquets.
The above-described tourniquets are designed for use with a dual port cuff. The inflation and deflation mechanism is connected to one port of the cuff, and the pressure sensing means is connected to the other port of the cuff. This design is preferable to a single port design since it insures that the pressure sensor is responding to the pressure in the cuff, and not merely the pressure of the pressurizing means. The prior art devices also include a means intended to detect occlusions between the pressurizing means in the cuff and the pressure sensor in the cuff. The most common such occlusion is a kink in either the line between the pressurizing means and the cuff or the line between the pressure sensing means and the cuff. Thus the occlusion detector has generally become known as a kink detector.
The prior art kink detectors consist of a system which sounds an alarm if the pressurizing means attempts to inflate or deflate the cuff and the pressure sensing means does not respond as it is expected it should.
The prior art kink detectors respond to a number of other system defects in addition to occlusions. For example, they may respond to problems in the pumping system, the sensing system, or leaks in the system. Such non-specific alarms may result in delays in detecting the precise cause of the alarm. Such delays are undesirable in the surgical environment. Further, the prior art occlusion detection systems must be sophisticated, since they must be able to accurately anticipate what the response of the pressure sensor should be to activities of the pressurizing system. This response is not always simple because the pressurizing system and the sensing system are separated by a considerable length of narrow tubing and the cuff, which results in a delay between the activity of pressurizing system and the response of the sensing system.